Field of the Invention
The invention is concerned with winches having a powered rotatable drum for winding in and releasing a cable or the like and more particularly to a winch system of the type in which the drum is driven and controlled by means of fluid pressure-operated clutches and brakes.
Prior application Ser. No. 334,354 of L. F. Yates et al., filed Feb. 21, 1973 for "WINCH WITH FREE-WHEELING DRUM" assigned to the assignee of the present application and referred to in U.S. Pat. No. 3,841,608, discloses a winch assembly which is driven by an engine through a drive train having a normally disengaged input clutch which engages in response to fluid pressure to reel in cable. The drive train also includes a normally engaged brake for immobilizing the winch drum but which releases in response to fluid pressure in other modes of operation. In addition to the Brake-On and Reel-In modes of operation, the brake alone may be pressurized to effect a Brake-Off mode in which load forces pulling on the line may unwind cable against the limited resistance created by the drag of the drive train components. This limited resistance prevents excess unwinding of cable by a load, from drum momentum or other causes, but is sufficiently strong that it is difficult or impossible to withdraw cable manually while such resistance is present. Accordingly, the drive train connects to the winch drum itself through a disconnect clutch which is normally engaged but which may be disengaged by fluid pressure to allow manual reeling of cable from the drum without working against a substantial resistance. This form of winch assembly is highly useful on a log skidder vehicle, for example, which is used to drag logs from the site of a lumbering operation and also has substantial advantages in other contexts.
Prior U.S. Pat. No. 3,841,608 discloses a hydraulic control system for a winch assembly of this kind in which a manually operated control valve may be shifted between a series of positions to pressurize and depressurize appropriate ones of the clutches and brake of the drive train in order to accomplish the several operational modes described above. The valve settings include Reel-In, Brake-On, Brake-Off and Free-spool and are realized by movement of a control lever or the like. For safety reasons as well as for convenience of operation, centering springs urge the control valve towards the Brake-On position so that if the operator releases his control lever or the like, the winch is automatically immobilized.
The operator of these winch systems must pay careful attention to the position of his control lever or the like in order to control movement of a load in a safe and efficient manner. It is particularly important to avoid movement of the lever into the Disconnect position through misjudgment while a load is pulling on the cable since momentum and overtravel may cause an excessive amount of cable to be released, creating unwanted slack, when dropping of the load stops or slows. Diversion of the operator's visual attention in order to guard against this occurrence is undesirable in many cases, particularly in such usages as on a log skidder where the operator must pay attention to controlling the vehicle itself in addition to operating the winch.
In order to guard against inadvertent movement of the control lever into the Free-spool position, the lever has usually been constrained to pivot along a slot in a console which includes an angled section whereby sideward movement is needed before the lever movement can be continued into the Free-spool position from the adjusted position. This arrangement accomplishes the objective of alerting the operator when the lever approaches the Free-spool position but it also undesirably complicates lever manipulation and delays shifting into the Free-spool mode at a time when fast action may be required.
Prior copening application Ser. No. 574,807 of Edward E. Flesburg, filed May 5, 1975 for "Winch and Fluid Control System Therefor" and assigned to the assignee of the present application discloses a winch system having a plurality of modes of operation, including a Free-spool mode in which there is little resistance to turning of the winch drum, which are initiated by movement of a single control lever. Means are provided which enable the operator to determine when the control lever is approaching the Free-spool position without necessarily relying on visual observation for this purpose and without complicating the lever movement pattern.
Generally, prior art vehicles supporting winches have had a pump driven by an engine shaft with the pump being positioned adjacent the engine. Thus, the pump has been on the tractor side of an articulation joint when the vehicle is articulated. The winch, on the other hand, has been on the trailer side of the articulated joint. This has required the provision of hydraulic lines which cross the articulated joint. The pressurized fluid from these hydraulic lines has been used to drive a hydraulic motor or the like which drive an input shaft of means for selectably transmitting rotary motion to the winch. The pressurized fluid is generally also used to activate various clutches and brakes of the means for selectively transmitting rotary motion to the winch. Passing hydraulic lines across an articulated joint, however, creates very serious construction and operation problems. Accordingly, the present invention provides a vehicle supported winch wherein the source of pressurized fluid which operates the clutches and the brakes of the winch system comprises pump means on the trailer side of the articulation driven by the transmission of the vehicle rather than by the engine and wherein the coupling to the transmission and the pump are generally on the trailer side of the articulation and via a single shaft thus eliminating hydraulic line coupling problems from the input shaft to the rotary motion transmitting means and from the pump shaft to the pump both proceeding from the tractor. The use of transmission driving for the pump means, however, introduces another problem, namely, that the transmission can slow down and stall as it is subjected to heavy loads even though the engine continues to turn. This is especially true with fluid transmissions. To solve this problem it has been found necessary to use in combination with the pump means driven by the transmission an accumulator for storing fluid pressure produced by the pump means when it functions and for supplying fluid pressure when functioning of the pump means is retarded. Thus, the advantages of driving the pump means by the transmission can be realized without the disadvantages which would be inherent therein without the use of an accumulator.